Conventional devices that are capable of obtaining tomographic images using ultrasound waves, which are ordinary elastic waves, have a transmission unit for transmitting ultrasound waves, which are elastic waves, to a sample, a reception unit for receiving reflected waves, and scanning means for scanning transmission and reception waves. There is also provided means for converting the received reflection signals to brightness signals, and visualizing the signals. The interior of a sample is thus observed using a time-series tomographic image obtained by way of the above means. In one form of the above device, the abovementioned scanning means scans ultrasound waves, up and down, left and right, as a result of which a three-dimensional image can be obtained.
Living organisms are one example of subjects that can be examined by ultrasound waves. Ultrasound waves are advantageous in terms of, for instance, real-time characteristics, simplicity and non-invasiveness, and are thus widely used for observing the interior of organisms.
Ultrasound waves that are used for in-vivo observation are transmitted and received by way of a plurality of electromechanical transducer elements (mainly piezoelectric elements, capacitive ultrasound transducer elements and the like).
During transmission, ultrasound waves are generated, converging at a focus position, through application of an electric signal to a plurality of elements, in a time-staggered fashion, in such a manner that the phases of the ultrasound waves coincide at the focus position. The region traversed by ultrasound waves generated according to such driving is centered about a straight line that joins the focus position and the central positions of the plurality of elements that are driven. A transmission beam is formed so as to pass through this region. During reception, the time delays corresponding to the focus position are corrected and added, for the electric signals generated in the plurality of elements on the basis of the received ultrasound waves. Reflected signals of the ultrasound waves at the focus position are acquired as a result. Adding electric signals from the plurality of elements yields waveform data that holds a waveform of the ultrasound waves. An envelope of the received waveform data is acquired next (this is also referred to as environment detection), whereby the received waveform data is converted to intensity data. Lastly, this intensity data is thinned and/or rounded, in accordance with the pixels of the image on which the intensity data is to be displayed, followed by interpolation, as the case may require, to form an image thereby. The focus position during reception can be modified in real time. The region in the focus position as generated in the reception process for the transmission beam constitutes a region that is traversed by the reception beam.
In an ultrasound diagnosis apparatus, controlling transmission and reception in such a way enables transmission of ultrasound waves to a portion that is to be observed, reception of resulting reflected waves, and imaging of the interior of the organism. The straight-line regions acquired based on the transmission beams and the reception beams are called scanlines. An image is formed by arranging a plurality of scanline data.
Ultrasound waves generated according to the above principles enable non-invasive imaging of the interior of an organism, and hence ultrasound waves are widely used for detecting various situations in a body. One such instance is the detection of high-reflection bodies, such as calculi or the like. A widely practiced method for detecting calculi in medical facilities involves detecting the presence of calculi depending on whether an acoustic shadow appears on images of deeper sites behind a calculus, i.e. on a farther side from the probe. An acoustic shadow is a shadow portion that arises through failing of an image to be formed behind a high-reflection body, since the ultrasound pulse does not reach behind the high-reflection body, while the reception beam is blocked by the high-reflection body.
Patent Literature 1 (PTL 1) discloses an ultrasound device in which a correlation between adjacent scanlines is acquired, in order to set scanline density, and a transmission beamformer or reception beamformer is controlled depending on the result.
Patent Literature 2 (PTL 2) discloses an ultrasound device in which tissue contours are extracted on the basis of image data.
Patent Literature 3 (PTL 3) discloses a signal processing apparatus wherein there is acquired received waveform data of a plurality of scanlines through scanning of an elastic wave beam through the interior of an object, and wherein signal processing is performed in order to form a tomographic image of the object on the basis of received waveform data of the plurality of scanlines, the apparatus comprising: an inter-scanline correlation calculation unit that calculates a correlation value of received waveform data between a first scanline and a second scanline having a predetermined correlation with the first scanline, for each of a plurality of positions on the scanline; and a correlation change position extraction unit that extracts, from among the plurality of positions on the scanline, a position at which a singular region is likely to be present, in the form of a position at which the correlation value takes on a value that differs from a predetermined value.
Patent Literature 4 (PTL 4) discloses an ultrasound imaging apparatus in which linear boundaries in tomographic images, or boundary surfaces in three-dimensional information, are detected by using phase information of reflected waves. Patent Literature 4 (PTL 4) discloses specific means that involves displaying contour information in an object, as well as boundaries contiguous to an object, by obtaining a time at which a cross-correlation function between scanlines is maximal, from designated positions, and by linking positions that are obtained on the basis of the obtained times.
Non-Patent Literature 1 (NPL 1) discloses a method that involves obtaining correlation values between adjacent scanlines, and extracting calculus positions on the basis of changes in the correlation values for a same depth. Non-Patent Literature 1 (NPL 1) discloses also a method for enhancing positional precision upon calculus extraction by applying a pattern matching method to changes in correlation values for a same depth.